With the coming of HTML5 and Blogger platform changes here and there, I found my HTML/CSS noob of a self largely outdated as I wanted to customize a new blog for my paper / pop-up works. After some light research I managed - roughly - to do what I wanted. For my information and record (and yours), a few helpful links:

Split your header in two (painless)

This was found, after some wandering, on TellForceBlog (thank you).
Just in case it should go down, here is a screenshot: